This invention relates to a receiver for receiving radio signals, having an antenna array comprising a plurality of antenna elements and a feed for feeding the antenna elements.
The invention also relates to an antenna array for such a receiver.
Receivers comprising antenna arrays are widely known. They can be used in situations in which a large gain factor in a specific direction is wanted. One of these situations is in a system for cellular TV. In such a system a transmitter or a small number of transmitters per cell transmit signals. The receivers are directed to one of the transmitters in order to receive the signal well.
A problem which exists especially in urban environments is the problem of multipath fading. This means that signals due to reflections reach the antenna via a plurality of different paths. Due to transmission time differences between the signals, there will be phase differences between them. Because of this, there will be some points in which the signals are added and some points in which the signals are cancelled. Therefore an interference pattern of the received signal power level with maxima and minima (nulls) will occur. When the antenna array is in or near a minimum this will result in a bad signal reception.
The problem of multipath fading is also known from other fields, e.g. cordless telephony. A solution known from that field is to have two antennas separated by a certain distance. In the situation where the first antenna is switched on and the received signal is bad, the antenna probably is near a minimum. By switching it off and switching the second antenna on, almost always a better reception can be obtained.
However, this is not an attractive solution for a receiver with an antenna array since the duplication of a whole array is awkward and expensive. Furthermore, this solution takes a relatively large amount of space.